(1) Field of the Invention
The present invention relates to a test disk used to test a playing ability of a disk player by reproducing signals from defect patterns of recording areas of the test disk, and to a method of production of the test disk.
(2) Description of the Prior Art
A disk storage medium such as a compact disk that is housed in a compact disk player might have in the recording areas several physical defects: black dots, dust, fingerprints, stains, lack of data pits, flaws, etc. In particular, the black dots may appear with foreign matter included in the recording areas of the disk storage medium during the disk production, and dust, fingerprints and stains may stick to the disk surface.
Compact disk players are primarily designed to reproduce music signals from a compact disk, and it is necessary to test the playing ability of compact disk players before the release from the assembly plant. A test disk is used to test the playing ability of the compact disk players during inspection processes after the assembly is completed. That is, the test disk is placed into the compact disk player during the inspection processes, and the playing ability of an assembled compact disk player is tested by reproducing signals from the recording areas of the test disk during inspection processes. The playing ability is evaluated based on the reproduced signals from the test disk.
A primary object of the test disk is to simulate the defects which might be included in the recording areas of the disk storage medium, when signals are reproduced from the recording areas of the test disk. To attain this object, the recording areas of test disks are formed with defect patterns which include: 1) interruptions that are defect patterns used to simulate the lack of data pits and the flaws mentioned above; 2) black bands that are defect patterns used to simulate the black dots, the dust and the stains mentioned above; and 3) fingerprint patterns that are defect patterns used to simulate the fingerprint mentioned above.
The recording areas of a test disk may be composed of music signal tracks in which music signals are recorded, and sine-wave signal tracks in which sine-wave signals are recorded. As described above, the playing ability of compact disk players is tested based on the reproduced signals from the test disk. For example, an inspecting person may evaluate the playing ability of a compact disk player which has been assembled in the assembly plant, by hearing music sound obtained from the music signals reproduced from the music signal tracks of the test disk wherein defect patterns are included. This testing is performed by the hearing ability of the inspecting person. Also, the playing ability of the compact disk player may be evaluated by electrically measuring a frequency obtained from the sine-wave signals reproduced from the sine-wave signal tracks of the test disk wherein defect patterns are included, by use of a waveform measuring instrument such as an oscilloscope.
Therefore, the test disk is used to test the playing ability of the disk player by reproducing signals from the recording areas of the test disk containing the defect patterns. Hereinafter, the defect patterns from which the signals are reproduced for testing the playing ability of the disk player are the interruptions mentioned above, unless otherwise specified.
In order to make the testing of the playing ability of the disk player reliable and accurate, it is desirable that the playing ability of the disk player is tested with a test disk having defect patterns which are arranged at random in the recording areas of the test disk. Therefore, it is necessary to produce a test disk having such defect patterns arranged at random, for use in the testing of the playing ability of the disk player.
In conventional methods of production of test disks, the test disks are produced from plastics such as polycarbonate through injection molding by use of a stamper. The stamper is a base on which the test disk is produced through injection molding. However, in the conventional methods, defect patterns are formed on the stamper by manually scratching the corresponding portions of the stamper by hand, or by machining the corresponding portions of the stamper by use of machining equipment.
To produce a test disk by use of a stamper with the manually scratched portion, a relatively large amount of labor and time is necessary and the cost of the production of the test disk will be raised. The efficiency of the inspection by the inspecting operator will become lower. In addition, when the defect patterns are manually scratched on the stamper, it is likely that the defect patterns are arranged in the recording areas of the test disk with a deviation, that is, the test disk may have some portions with defect patterns being densely arranged and the other portions with defect patterns being sparsely arranged. Therefore, the testing of the playing ability of disk players performed with such a test disk may become inaccurate due to the deviation of the defect patterns within the test disk.
On the other hand, when a test disk is produced by machining the stamper by use of the machining equipment, it is impossible to realize the test disk having defect patterns arranged at random in the recording areas of the test disk. The defect patterns within such a test disk are arranged in one direction only, and they are spaced from one another at fixed intervals. It is difficult to simulate the defects which might be included in an actual compact disk, by reproducing signals from the test disk.